resolved some issues

Signed-off-by: Xiaoxuan Wang <[email protected]>

content/oci/oci.go

@@ -403,12 +403,25 @@ func (s *Store) writeIndexFile() error {
 }
 
 // GC removes garbage from Store. The garbage to be cleaned are:
-//   - garbage blobs in the storage whose metadata is not stored in Store.
 //   - unreferenced (dangling) blobs in Store which have no predecessors
+//   - garbage blobs in the storage whose metadata is not stored in Store
 func (s *Store) GC(ctx context.Context) error {
-	s.sync.RLock()
-	defer s.sync.RUnlock()
+	s.sync.Lock()
+	defer s.sync.Unlock()
+
+	// clean up dangling layers in Store
+	danglings := s.graph.GetDanglingLayers()
+	for _, desc := range danglings {
+		// do not remove existing manifests in the index
+		if _, err := s.tagResolver.Resolve(ctx, string(desc.Digest)); err == errdef.ErrNotFound {
+			// remove the blob and its metadata from the Store
+			if err := s.deleteNode(ctx, desc); err != nil {
+				return err
+			}
+		}
+	}
 
+	// clean up garbage blobs in the storage
 	rootpath := filepath.Join(s.root, "blobs")
 	return filepath.Walk(rootpath, func(path string, info fs.FileInfo, err error) error {
 		if err != nil {
@@ -421,8 +434,7 @@ func (s *Store) GC(ctx context.Context) error {
 			if err != nil {
 				return err
 			}
-			exists, desc := s.graph.ExistsInStore(blobDigest)
-			if !exists {
+			if exists := s.graph.Exists(blobDigest); !exists {
 				// remove the blob from storage if it does not exist in Store
 				err = os.Remove(path)
 				if err != nil {
@@ -431,11 +443,6 @@ func (s *Store) GC(ctx context.Context) error {
 					}
 					return err
 				}
-			} else if !s.graph.HasPredecessors(blobDigest) {
-				if _, err := s.tagResolver.Resolve(ctx, string(blobDigest)); err != nil {
-					// remove the blob and its metadata from the Store
-					s.deleteNode(ctx, desc)
-				}
 			}
 		}
 		return nil

content/oci/oci_test.go

@@ -2412,7 +2412,7 @@ func TestStore_GC(t *testing.T) {
 	appendBlob(ocispec.MediaTypeImageConfig, []byte("config"))         // Blob 0
 	appendBlob(ocispec.MediaTypeImageLayer, []byte("blob"))            // Blob 1
 	appendBlob(ocispec.MediaTypeImageLayer, []byte("dangling layer"))  // Blob 2, dangling layer
-	generateManifest(descs[0], descs[1])                               // Blob 3
+	generateManifest(descs[0], descs[1])                               // Blob 3, valid manifest
 	appendBlob(ocispec.MediaTypeImageLayer, []byte("garbage layer 1")) // Blob 4, garbage layer 1
 	generateManifest(descs[0], descs[4])                               // Blob 5, garbage manifest 1
 	appendBlob(ocispec.MediaTypeImageConfig, []byte("garbage config")) // Blob 6, garbage config

internal/graph/memory.go

@@ -175,15 +175,19 @@ func (m *Memory) index(ctx context.Context, fetcher content.Fetcher, node ocispe
 	return successors, nil
 }
 
-// ExistsInStore returns if a blob denoted by its digest exists in the memory.
-// The descriptor associated with the digest is also returned.
-func (m *Memory) ExistsInStore(dgst digest.Digest) (bool, ocispec.Descriptor) {
-	desc, exists := m.nodes[dgst]
-	return exists, desc
+// Exists returns if a blob denoted by its digest exists in the memory.
+func (m *Memory) Exists(dgst digest.Digest) bool {
+	_, exists := m.nodes[dgst]
+	return exists
 }
 
-// HasPredecessors returns if a blob denoted by its digest has any predecessors.
-func (m *Memory) HasPredecessors(dgst digest.Digest) bool {
-	_, hasPredecessors := m.predecessors[dgst]
-	return hasPredecessors
+// GetDanglingLayers returns the dangling (unreferenced) layer nodes in the memory.
+func (m *Memory) GetDanglingLayers() []ocispec.Descriptor {
+	var danglings []ocispec.Descriptor
+	for key, desc := range m.nodes {
+		if _, exist := m.predecessors[key]; !exist {
+			danglings = append(danglings, desc)
+		}
+	}
+	return danglings
 }